Communication system



Nov. 14, 1944. H. GoLDBx-:RG E-rAL COMMUNICATION SYSTEM Filed Feb.` 172l l9l12 2 Sheets-Sheet l T M ATTORNEY.

Nov. 14, 1944.

H. GLDBERG' ETAL COMMUNICATION SYSTEM Filed Feb. 12, 1942 2 Sheets-Lheet 2 Patented Nov. 14, 1944 `Harold Goldberg, Frank H. Slaymaker, and J.

Russell Stewart, Rochester, N. Y., assignors to The Stromberg-Carlson Telephone Manufacturing Company, Rochester, N. Y., a corporation of New York Application February Il2, 1942, Serial No. 430,592

8v Claims.

tems employing radio transmitting and receiving apparatus and is `characterized as employing apparatus and circuits for an improved methodof signalling by means of modulated carrier currents or waves.

The invention is particularly useful when applied to a communication system, whereby it is possible for the users to move about and, by means of a4 portable transmitter and receiver carried by such users be able to communicate with each other through the intercommunicating system and without `the need of any power supply or Wire connection to or from the equipment which they carry.

This invention will be shown and described as being applied to an intra-tank communicating system within an enclosure. `It will be understood that it may nd use in numerous fields of service, for example, in military operations where it is necessary to employ portable telephone apparatus which must be characterized by reasonably high power and efciency, lightness, com# pactness, resistance to mechanical shocks and rough usage generally, and also by simplicity and convenience of operation and maintenance.

By way of concrete illustration and `in order that `the invention may be fully understood by those skilled in the art, an especially desirable form of apparatus and circuits embodying the principles of the invention is shown in the accompanying drawings and will be described in detail.

Fig. 1 is a block diagram illustrating the arrangement of the various components of the complete system;

Fig. 2 shows the circuit of the lator;

Fig. 3 shows the circuit of the portablereceiver;

Fig. 4 shows the circuit of a combined portable receiver and portable modulator;

Fig. 5 shows the circuits of the absorption modulated transmitter and its antenna, the remodulator and the plate modulated transmitter and its antenna; i

Figs. 6 and 7 graphically represent respectively a high frequency wave with a low degree of modulation and a high frequency wave with a high degree of modulation.'

In Fig. 5 the absorption modulated transmitter is shown connected to the remodulator by means of wire I0 and the remodulator is shown connectedto the plate modulated transmitter by means of wire Il. `These same interconnections are indicated in Fig. 1` by means of the same reference characters.` z

portable modu-` V This invention relates to communication sys- One basic principle of operation of our invention is based on the phenomenon that the electromagnetic'eld due to any source is determined not only by the characteristics of the source, but also by the position, size and electrical properties of all conductors and dielectrics within a space surrounding that source.

Another basic principle of operation of our invention is `b ased on the phenomenon that a variation in resistance or impedance may be reflected from one circuit into another, without any conductive connection'betweenthe two, by means of inductive coupling.`

It is accordingly an object of our invention to set up an electro-magnetic field from a source of high frequency oscillations and to vary or modulate that eld byf4 changing the electrical properties of the circuits and rconductors within Consequently;` a further object of our inven tionis'the provision, in a communication system, of a high frequency oscillator which sets up an electro-magnetic eld,.and meansincluding one or more portable conductively isolated telephone transmitters or other means. for absorptively modulating the field whereby modulated energy is radiated.

Another object of our invention is to apply high frequency oscillations, from a high frequency source, to one antenna or other radi-ating means and to varyv or modulate` the high frequency waves in this one antenna circuit by reflecting variations in resistance'or impedance from another antenna into 'this' one antenna circuit by means of inductive coupling.

Another object-of our invention is the provision of a communication system outlined above, in which several modulators (telephonel transmitters or other means) with no outside conductive connectionmay be carried about and each may function to modulate the electro-magnetic field, whereby telephone inter-communication may be accomplished by the 'further-provisin of conductively isolated and iaortaltbleA receivers which will respond tothe modulated energy of the modulated electro-magnetic eld.

modulation, whereby increased power may be provided.-

Other objects of our invention willbecome apparent upon reading the following description taken in connection with the drawings.

The complete system, schematically illustrated s in Fig. 1 for purposes of convenience indescription, may be divided into an absorption modulated transmitter and associated portable modulator, al

' quency field is absorptively modulated.

remodulator and a plate modulated transmitter and associated portable receiver, with the various components Ain the `GCimplete system appropriately labeled.l v u v TheI absorptionV `modulated.transmitter comprises a conventionalV oscillator, oscillating at frequency FI, a .powerradio frequency' amplier, preferably a'pentode tube, operating as a vclass A amplier, the output of the amplifier being connected to loopantennaglll; which consists of one or moreturns-ofefwire strung around the tank walls.-

The remodulator isconnected to the output of the yradio frequency amplifier:v of the absorption modulated transmitteriand. comprises `a conventional. detector, a. conventional; audio frequency amplifier and a modulator, a1l indicated by block diagrams in Fig.. 1. f

The plate modulatedv transmittercomprises a highfrequency oscillatoroperating, at a different frequency, F2, fromi'thatlof the osoillatorof the absorption modulated transmitter.. Thetplate modulated transmitter alsocomprises a buffer and aclassffCwradio lfrequency amplifier, .all as illustrated by block diagrams.

-The portable modulator, illustratedin Fig-2, comprises an inductance liz-'Which'ma'y be worn about the body'offthe user',-for example -by being sewed inthe users' belt.- The -portablemodulator 'also comprises v amicatuning2 condensery C I and a carbon microphone M: -'lfhe inductance or antennajLZ-is shown-Withgavariable connection to the modulator 1M: This is so that the modulator or microphone maybe tapped into the loop L2 at the right `vnumberjof tu'rns for'providing-the most veffective modulation.

The portable receiver illustrated in Fig. i3 comprises a tuned circuit consisting of induotance L4, which may be in theform ofa small loopv antenna Worn by the user, tfo'r'exarriple by being sewed 1n thelusers belt,A tuning condenser C2, a diode detector V4; a headset HS and bypass condenser C3.

It" will be understood that,v jwhile only a single portable modulatorjand a single portable receiver are shown, a plurality ofeither `or both of these devices may `be operated in the present system.

Furthermore, a 'rectierX may 'be used in Fig. 3

in placev ofy the tube, as .illustrated in'dotted lines.' This rectilier x'nay'be'of the dry plate or other type..r4 .I

Fig. '4 illustratesja combined modulator or transmitter; and yreceiver, comprising aV telephone transmitter IAM, a `'headset ',IHS, n a bypass condenser lC3,indicta1ices'or`loop antennas [L2 and iLa'tuned by 'Condensers' ICI ajndflcz' andy a diode detector |V4. It willbe understood'that the vcomunit of the modulator and receiver illustrated as separate units in Figs. 2 and 3.v

In our communication system, a radio frequency field is'set up Within the tank by means of the first stationary transmitter and modulation is accomplished by yaltering the absorption -characteristics of a portable modulator'.v When a member of the tank crew talks into his microphone, the sound Waves vary the resistance of the microphone which, in turn, alters the amount of power which the modulator unit absorbs from the radio frequency eld.' Consequently, this radio fre- It has been found possible to detect the modulation of this radio frequency eld by means of a portable receiver such as that illustrated in Fig. 3. However, the low percentage of modulation produced by absorption alone makes the volume of the signal at the headset insufficient to oVerTride any large amount of interference or extraneous noise.

We have, therefore, increased the volume at the headset by first. detecting the modulation of the radio frequency-field by means of a detector and an audio amplie'r, illustrated in Figs. 1 and 5 by means of block diagrams. Then the output of the audio amplifier is used to modulate the output stage ofa secondradio-frequency transmitter which operates on a different frequency from 4the first transmitter. This provides sucient gain to modulate thesecond transmitter to around 100%. Fig.' 6'A illustrates lthe modulated radio frequencyl FI", `modulated to a low degree, for example 3%,and' Fig. 7' illustrates the modulated radio frequency F2,v modulated to a substantially higher degree, for example 100%.. l

The loops L2- and L4 of the DOrtable modulator and portable receiver may be includedfin one belt. Furthermore, the headsetand'microphone may be made up in va single unit which plugs into an apalrtatus compartment mounted on the wearers In the operation of, the. system illustrated, the

relative position or theportable loopsfLZv and L4 y and the main loops Lly andLS. results in the portable modulator being coupled' rather loosely to loop. L1 so 'that any .change-inthe resistance of the carbonbutton of microphone M, due to sound e'ntering'the microphone; shows up in a cha-nge in the apparent resistance. of. loop LI. Consequently, the radio ireguencypotential across the terminals of loop,v LI ismodula-ted by talking into the microphone-andthe iield of loop Ll is; modulated as a result. Condensers C4 and Cfof Fig, 5 serve as a Voltage divider to provide the, proper vltage for the remodulator. The detector oi the remodulator. circuit is 'tuned to frequency Ft and the audio,` frequency'. amplifier'. togethery with modulator tube V2', ,acts as fa conventional modulator to vary the plataand; screen supply voltage ofthe output tube V3.;y oflfth'e plate modulated transmitter.

The plate modulated transmitter is driven by oscillatorFZ, operating. atf'requency; F2, the amplifier consisting of-.pentod'e tube V3; operating as a. class C amplierfand; whichis plate modulated from the remodulator. by. WayfOf-Conduto' Ill) and the loop. L31 which isi tuned by C011- denser ICB. f v Y f y It, will be understood thatV the :remodulator andr l the plate modulatedltransmitter may be omitted ponents illustrated 'in`Figl4"make` up a single 75 and stili' the 'system wnicperatealthough the sig-. nals are modulated at ra verylow deg-ree and will be weak, We prefer to use the system illustrated in Fig. 1, since this provides exceptionally good signal strength. Y y

In tests of this system, it was determined that satisfactory operation could be obtained by using v conventional'electronic oscillators for supplying 5 frequencies FI and F2, by usinga SFB vacuum tube for tube VI illustrated in Fig. operating as a class A stage, by using a GF6 tube operating'in class C for tube V3 in Fig. 5 and by using. a pair of SLG tubes in the output of a three stage audio frequency amplifier. It was further determined that frequency Fl could be 1100 kc. and frequency F2 could be 2200 kc. We do not wish to be limited to these specific values and devices, but cite'them to show what was used in one actual operative specimen.

` While a particular type of remodulator has been illustrated for increasing the degree of modulation, we have found that a modulation boosterV is especially adaptable for stepping up the degree f modulation. Such a .booster modulator is shown in the pending applicationof Frank H. Slaymaker, Serial No. 432,052, filed February 23, 1942, and assigned to the same assignee as this invention. l

Although we have illustrated and described `only a single embodiment of our invention, numerous modifications in addition to those referred to, as well as additional advantages thereof, may be apparent to those skilled in the art. Our invention, therefore, is not to be limitedexcept insofai` as necessitated by the prior art and by the spirit of the appended claims.

What we claim is:

l. The method of communication which consists in generating a first radio frequency alternating current, radiating electro-magnetic waves of said first radio frequency from a radiator circuit, generating audio frequency signals, absorptively modulating said first radio frequency electro-magnetic waves by reflecting said audio signals into said radiator circuit, generating a second radio frequency alternating current, radiating electro-magnetic Waves of said second radio frequency, modulating said second radio frequency as a function of said modulated first radio frequency, and receiving said audio frequency signals by demodulating the signals produced by the modulation of said second radio frequency.

2. In a wireless signalling system, a first source of high frequency energy, a first stationary antenna circuit tuned to the frequency of said first source, means for connecting said first source to said first stationary antenna circuit whereby high frequency electro-magnetic primary Waves of the frequency of said first source are radiated, a portable antenna circuit coupled to said first stationary antenna circuit, means including a microphone for controlling the radio frequency electromagnetic eld of said first stationary antenna circuit by changing the resistance of said portable antenna circuity in accordance With audio frequency signals actuating said microphone whereby said primary waves are modulated, a second source of high frequency energy, a second stationary antenna circuit tuned to the frequency of said second source, means for connecting said second source to said second stationary antenna circuit whereby high frequency electro-magnetic secondary waves of the frequency of said second 70 source are radiated, means controlled by said primary modulated waves for modulating said secondary Waves, and means for demodulating and receiving said secondary waves.

3. In a wireless signalling system, a first source 75 ofihighfrequency energy, 'a first stationary antennacircuit tuned to thefrequency of said first source, means forconnecting said first source to said stationary antenna circuit whereby high frequency electro-magnetic primary Waves of the frequency of saidiirst source are radiated, a plurality of portable antenna circuits coupled to said first stationary antenna circuit, means including a .plurality of microphones for controlling the radio frequency electro-magnetic field of said first stationary antenna circuit by changing the resistance of said portable antenna circuits in accordance with audio frequency signals actuating said microphones whereby said primary waves are modulated, a second source of high frequency energy, a second stationary antenna circuit tuned to the frequency of said second source, means for vconnecting saidsecond source to said second stationary antenna circuitiwhereby high frequency electro-,magnetic secondary Vwaves of the frequency of said second source are radiated, means controlled by said primary modulated waves for modulating `saidsecondary waves, and means for demodulating and receiving said secondary waves. 4. In a Wireless signalling system, a first source ofhigh frequency energy, a first stationary antenna circuit tuned to the frequency of said first source, means for connecting said first source to said first stationary antenna circuit whereby high frequency electro-magnetic primary waves of the frequency of said first'source are radiated, a first portable antenna circuit tuned to the frequency of 'said` first source and coupled to said first stationary antenna circuit, means including a microphone for controlling. the radio frequency electro-magnetic field of said first stationary antenna circuit by changing the resistance of said first portable antenna circuit in accordance with audio frequency signals actuating said microphone whereby said primary waves are modulated, a second source of high frequency energy, a second stationary antenna circuit tuned to the frequency of said second source, means for connecting 'said second source to said second stationary antenna circuit whereby high frequency electro-magnetic secondary waves of the frequency of said second source are radiated, means controlled by said primary modulated waves for modulating said secondary Waves, means including a second portable antenna circuit for demodulating said secondary Waves, and means for receiving said demodulated secondary Waves.

5. In a wireless signalling system, a, first source of high frequency energy, a first stationary antenna circuit tuned to the frequency of said first source, means for connecting said rst source. to said rst stationary, antenna circuit whereby high frequency electro-magnetic primary waves of the frequency of said first source are radiated, a first portable antenna circuit tuned to the frequency of said first source and coupled to said first stationary antenna circuit, means including a microphone for controlling the radio frequency electro-magnetic field of said first stationary antenna circuit by changing the resistance of said first portable antenna circuit in accordance with audio frequency signals actuating said microphone whereby said primaryywaves are modulated, a second source of high frequency energy, a second stationary antenna circuit tuned to the frequency of said second source, means for connecting said second source to said second stationary antenna circuit whereby high frequency electro-magnetic secondary Waves of the frequency of said second source are radiated, means controlled by said. primary` modulated waves for modulating said secondaryfwavcsv toy asfliigherdegrec-than said primarywaves-'f means including aseccnd portable antenna` circuit for demodu'lating said secondary: waves; and-meansfor receivingfsaid demodulatedfsecondary-waves.

:16. In amodulating system; afrstantennacircuit-supplied a by a source of` energy of.. ai first radio frequency, a; second'antenna:circuitfsupplied by a source of energy of asecondiradovfrequency, a nrst anda second inductive meansirespectively coupled tosaid rst andfsaidf second antennas, means VforI tuning said =rst 4antenna andI said rst inductivegmeansfto saidfirst radio frequency, means fortuning said second antenna and saidv second. inductiveJ means to said second radio frequency, aportabletelephone set, com .prising a telephone transmitter: and a-'telephone receiver,l means including said; telephone transclusionpof said modulatedwaves.

I 7. In combination, a rst antenna circuit and a-'second antenna circuit respectively supplied .with radio frequencycurrents of; a rst frequency and a second frequency, means for linter-connesting;r said; antenna circuitsmeans .y inductively ,coupleditotsaidv rst antenna. circu-it for absorp-g tively-'modulatingsaid rst radio lfrequency cur-f rentsin accordance with signals to be transmit. ted,.;means includingja vacuum Atube ampliiier and; said second antenna circuit for transmitting currentspof said lsecondv radio frequency,` and means -for varyingthe output of said vacuumv tube 'ampler as afunction'of the modulated rst radici-frequency currents, wlfierebyV remodulated radio frequencyl waves corresponding to said sigf nals are transmitted; i

. A8. In combination, a'irst antenna circuit and a second antenna circuit respectively, supplied with radio frequency currents of a rst frequency andaisecond frequency, means for inter-connect-v ingA said antenna circuits, means inductively coupled to saidrst antenna circuit for absorptively modulating said rst radio frequency cur.. rents-in accordance with signals to be transmitted; lmeans including a vacuum tube amplifier and said second antenna circuit for transmitting curquencywaves corresponding to said signals are transmitted, and means includingfa vacuum tube detectorv for receiving saidl signals.

HAROLD GOLDBERG. FRANK H. SLAYMAKER.. J. RUSSELL STEWART. 

